[GENERATORS] Update all the scripts to use python3

GeneratorInterface/Herwig7Interface/scripts/parallelization.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # This script sets up parallel jobs for the build, integrate and run
 # step when using Herwig with the CMSSW framework.

GeneratorInterface/LHEInterface/scripts/cmsLHEtoEOSManager.py

@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 
 from __future__ import print_function
 print('Starting cmsLHEtoEOSManager.py')

GeneratorInterface/LHEInterface/scripts/mergeLHE.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 from __future__ import print_function
 import logging